Low pressure process for manufacture of 3-dimethylaminopropylamine (DMAPA)

ABSTRACT

An improved process for the production of  3 -dimethylaminopropylamine in high purity from N,N-dimethylaminopropionitrile utilizing a low pressure hydrogenation process is described. The basic process comprises contacting the nitrile with hydrogen at low pressure in the presence of a catalyst under conditions sufficient to effect the conversion of the nitrile to the primary amine product.

[0001] This application is a continuation-in-part of and claims priorityfrom application Ser. No. 10/327,765, filed Dec. 23, 2002.

FIELD OF THE INVENTION

[0002] This invention is generally related to the manufacture ofdimethylaminopropylamine (DMAPA) from dimethylaminopropionitrile (DMAPN)using a hydrogenation process. More specifically, the invention isrelated to the use of a low-pressure diamine hydrogenation process forthe preparation of dimethylaminopropylamine fromdimethylaminopropionitrile with exceptionally high selectivity using asponge (Raney®) type catalyst with an alkali metal hydroxide solution.In particular, low-pressure hydrogenation of DMAPN to DMAPA using asponge nickel catalyst and a 50%/50% by weight mixture of sodiumhydroxide and potassium hydroxide at low temperature is disclosed.

BACKGROUND OF THE INVENTION

[0003] N,N-dimethylaminopropylamine (DMAPA,N,N-dimethyl-1,3-diaminopropane, 3-dimethylaminopropylamine) is animportant intermediate in the large-scale production of a variety ofindustrial processes. For example, DMAPA is an important intermediate asa surfactant for the production of soft soaps and other products, as anintermediate for the production of betaines and fatty amine oxides.N,N-dimethylamino-propylamine is also used as a starting product in theproduction of flocculating agents (by conversion to methacrylamide),road marking paints, and polyurethanes. DMAPA has also been shown toinhibit corrosion in boiler water treatment, and is an intermediate forgasoline and motor oil additives. Owing to DMAPA's wide utility, and thefact that the products it is associated with are produced at themulti-million pound per year level, there is the constant challenge toproduce the N,N-dimethylaminopropylamine in high yield and selectivity,due to the high costs associated with byproduct contamination.

[0004] One of the more common methods used for the commercial productionof aliphatic amines such as dimethylaminopropylamine has been thecatalytic hydrogenation of aliphatic nitriles using either batch ortrickle-bed hydrogenation techniques with the use of ammonia to inhibitsecondary amine formation. However, significant amounts of ammonia areneeded to carry out the reaction, and industrial handling of ammonia isexpensive and is associated with environmental problems. Over the years,several approaches attempted to identify optimum technology for theproduction of DMAPA.

[0005] U.S. Pat. No. 3,821,305 describes a hydrogenation process in theliquid phase at pressures of 20-50 atmospheres and temperatures between60° and 100° C. in the presence of a finely divided Raney® catalyst anda caustic alkali base. As specifically described therein, hydrogen andthe nitrile are fed into a liquid medium consisting of HMDA, water,caustic alkali base, and a catalyst, wherein the content of the base isin the range of 2-130 moles per mole of caustic alkali.

[0006] In U.S. Pat. No. 4,739,120, Zuckerman describes a process for thecatalytic hydrogenation of an organic nitrile group to a primary amineusing a rhodium catalyst and an inorganic or organic base having a pH of8 or greater. The reaction is described as being run in a two-phasesolvent system comprising an immiscible organic solvent and water.

[0007] U.S. Pat. No. 4,885,391 describes a process for the hydrogenationof C₄ to C₁₂ nitrites using a Raney® cobalt catalyst promoted withchromium in which the catalyst activity is maintained by the addition ofwater. The process is carried out at a temperature of about 80° to 150°C., and at a pressure of about 400 to 2500 psig, without the use of anycaustic bases.

[0008] U.S. Pat. No. 4,967,006 describes the use of ammonia in alcoholinstead of caustic base in order to have lower reaction pressures.However, the use of alcohol can be problematic, as it can sometimes bedifficult to remove and recycle depending upon the alcohol used, and itcan result in the formation of undesirable byproducts in the reaction.

[0009] Borninkhof et al. describe a process for preparing primary aminesby hydrogenation of mono and/or dinitriles in U.S. Pat. No. 5,571,943.As discussed therein, nitrites are hydrogenated in the presence of anickel and/or cobalt catalyst system on a support, optionally incombination with a solid, reaction medium-insoluble co-catalyst, whereinthe catalyst (and the co-catalyst) are non-acids.

[0010] U.S. Pat. No. 5,789,621 to Schnurr, et al. describes a processfor preparing amine-containing compounds by hydrogenation of nitritesusing a cobalt and/or iron-containing catalyst at an elevated (150° to400° C.) temperature and in a hydrogenation pressure range of 0.1 to 30MPa. The process is further described as being carried out in thepresence or absence of a solvent, and either batchwise or continuouslyin a fixed-bed reactor using either a downflow or upflow process.

[0011] In U.S. Pat. No. 5,840,989, Cordier et al. describe the use of aspecially doped Raney® nickel catalyst and a process of hydrogenatingnitrites to amines using this doped catalyst. A further embodiment ofthe process, as described therein, is the use of a partially aqueousliquid reaction medium, with the remainder of the reaction medium beinga solvent such as an alcohol or an amide.

[0012] U.S. Pat. No. 5,869,653 to Johnson describes a continuous processfor hydrogenating nitrites over Raney® cobalt catalysts in the absenceof ammonia, and in the presence of catalytic amounts of lithiumhydroxide and water. The reduction of nitrites to amines is carried outunder a hydrogen pressure of 1 to 300 bars, and at temperatures of 60°to 160° C. According to the description, the catalyst is eitherpre-treated with lithium hydroxide in order to achieve the desiredcatalytic effect, or the reaction is carried out with the lithiumhydroxide present in the reaction medium itself.

[0013] In U.S. Pat. No. 5,874,625, Elsasser describes an industrialbatch process for the hydrogenation of organic nitrites to primaryamines, using an aqueous alkali metal hydroxide, at least one Raney®catalyst, water, and hydrogen at temperatures between 150° and 220° C.and at hydrogen pressures between 250 and 2500 psi. According to thedisclosure, the improvement to the process comprises eliminating thesteps of drying the charge and adding water, and reducing the requiredwater in the system to about 0.2%.

[0014] European Patent No. EP 0316,761 to Kiel and Bauer teaches thatDMAPA can be made essentially free of the 1,3-propanediamine (PDA)by-product by using a sponge cobalt or nickel catalyst and a smallamount of either calcium or magnesium oxide and ammonia in order tocontrol the selectivity of the reaction in favor of the desired primaryamine. This patent also suggests that the process can be carried out attemperatures between 160° C. and 180° C. at 2200 psig with batchprocessing.

[0015] U.S. Pat. No. 6,281,388 to Goodwin, et al. describes a method forthe production of amines from nitrites using hydrogenation. The methodincludes the steps of feeding both hydrogen and a nitrile into a reactorcontaining a catalyst, water, and an inorganic base, and mixing thereaction medium to provide a uniform bulk concentration of nitrile in atleast one direction across the reactor in order to minimize reactorvolume. The described process can be carried out at pressures of 20-50atmospheres and 60-120° C., using a Raney® nickel catalyst and aninorganic base.

[0016] In U.S. Pat. No. 6,469,211, Ansmann et al. describe a process forthe continuous hydrogenation of nitrites and nitrites to primary aminesover an activated Raney® catalyst based on an alloy of aluminum and atleast one transition metal. This hydrogenation process is reportedlycarried out in the absence of ammonia and basic alkali metal compoundsor alkaline earth metal compounds.

[0017] US Patent Application Publication No. 2002/0058841 to Ansmann, etal. describes the activation and use of a special macroporous, shapedRaney® catalyst based on an alpha-Al₂O₃ alloy of aluminum and at leastone transition metal for use in the hydrogenation of nitrites to primaryamines. As detailed therein, the nitrile hydrogenation is carried out inan organic solvent such as DMF or NMP at a pressure of 10 to 300 bar.

[0018] The journal literature has also described approaches to thesynthesis of DMAPA using hydrogenation techniques. For example, Krupkaet al. in Coll. Czech. Chem. Commun. 2000, Vol. 65 (11), 1805-1819describe studies of the hydrogenation of 3-(dimethylamino)propionitrileover palladium catalysts. Effects of reaction conditions, types ofcatalyst, and the addition of ammonia or an amine into the charge on thehydrogenation selectivity are reported. According to the results, thesestudies indicated that the preferred catalyst is a Pd/SiO₂—Al₂O₃catalyst, and the formation of secondary and tertiary amines ispreferred in the hydrogenation of 3-(dimethylamino)propionitrile overpalladium.

[0019] Johnson, et al. in Catalysis of Organic Reactions, Vol. 82(2000), describes the use of lithium hydroxide modified sponge catalystsfor control of the primary amine selectivity in batch nitrilehydrogenations. The LiOH modified sponge cobalt catalyst used gave highprimary amine selectivity control in the conversion of nitrites toprimary amines, but high (750 psig) pressures were needed to effect thereaction.

[0020] However, even with the array of methods available for thesynthesis of DMAPA, most are not suitable for use in the commercialmanufacture of this compound. Many of the uses of DMAPA require that thecompound be of high purity and free of a number of by-products. Themethodologies described above, while generating the compound insynthetically acceptable yields, fail to meet the stringent requirementof the industry, e.g. producing a product in high yields that is >99%free of by-products.

[0021] Given the increased demand for highly pure DMAPA with minimal(<300 ppm) by-product contamination, there exists a need for a method ofmanufacturing N,N-dimethylaminopropylamine efficiently and in highselectivity (generally free of side products), in high production rates,in high yields, and with a purity greater than 99%.

SUMMARY OF THE INVENTION

[0022] The present invention is directed to an improved process for thelow-pressure hydrogenation manufacture of dimethylaminopropylamine from3-(dimethylamino)propionitrile with a selectivity greater than 99.50%.In a preferred embodiment, the basic process comprises contacting thenitrile with hydrogen in the presence of a sponge nickel catalyst underconditions suitable to effect conversion of the nitrile group to aprimary amine. The improvement in the hydrogenation process resides ineffecting the hydrogenation in the presence of a sponge nickel catalystincorporating inexpensive caustic hydroxide at low pressures (45-500psig) and temperatures (70-100° C.). To achieve a catalytic amount ofcaustic hydroxide in the sponge nickel, the reaction can be carried outwith the caustic hydroxide dissolved in water and dispersed in thereaction medium.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The use of alkaline substances in the presence of catalysts inorder to enhance the selectivity of primary amine formation during thehydrogenation of nitrites has long been known. Depending on the catalystand the conditions, nitrites can be transformed into primary, secondaryor tertiary amines, and most often a mixture of amine products isformed. For commercial reasons, only one of these products is thedesired product, and typically only the primary amine is the amine ofinterest.

[0024] Early studies in this area showed that adding ammonia to thehydrogenation mixture of a nitrile would strongly inhibit the formationof secondary amines, and other by-products. In the course of suchstudies, paths indicating the process for the hydrogenation of nitritesto amines has been proposed, showing both products and by-products. Forexample, it is known that a surface bound primary imine (1° imine)species is formed during the hydrogenation of the nitrile DMAPN. Thisspecies can be attacked by a primary amine (1° amine) such as DMAPA, andthen expels ammonia in a reversible step during the formation of thesecondary imine (2° imine). Hydrogenation of the 2° imine generates a 2°amine, 3,3′-iminobis(N,N′-dimethylpropylamine(di-(3-dimethylaminopropyl)amine). The formation of the 2° amine is forall practical purposes identical to the reductive amination of analdehyde. Also worth noting is that the presence of trace amounts ofimpurities from the starting nitrile DMAPN, such as dimethylamine (DMA)and acrylonitrile (AN), derived from the reverse Michael addition ofDMAPN to DMA and ACN, can generate problematic and difficult to removebyproducts such as N,N,N′,N′-tetramethyl-1,3-propanediamine (TMPDA). Avariety of other byproducts are also possible, such as n-propylamine,resulting from excess water in the reaction medium.

[0025] Of all of the byproducts which can potentially form in thecatalytic hydrogenation of DMAPN to DMAPA, none are more detrimental tocommercial product formation than the formation of TMPDA or the 2°amine. Both of these products are difficult to remove, and TMPDA isinseparable from DMAPA by distillation techniques. These byproducts canform additional byproducts when the contaminated DMAPA is used as anintermediate, and impart undesirable properties to the target products.Most recently, a large new DMAPA market has developed which requiresDMAPA as an intermediate containing less than 300 ppm TMPDA.

[0026] Since the product amine of interest, e.g.N,N-dimethylaminoproplyamine, is typically produced at the multi-billionpound per year level, Industry's challenge is to produce the product inhigh yield and selectivity because at these high volumes, even a fewtenths of a percent represents a significant byproduct removal anddisposal problem. From an economical standpoint, these byproducts canbecome unmanageable and costly to dispose of unless there is acommercial use for the byproducts. Consequently, it is beneficial todevelop improved and optimized technology for controlling theselectivity and yield of the primary amine product during thehydrogenation of N,N-dimethylaminopropionitrile.

[0027] It has been found, as described herein, that the incorporation ofa Group IA alkali metal hydroxide, or mixture thereof, in addition to asponge nickel catalyst, allows for increased control of the selectivitywhile hydrogenating DMAPN to DMAPA. The process can be carried out atlow hydrogenation pressures and temperatures, thereby increasing boththe yield and the selectivity in favor of the desired primary amine,3-dimethylaminopropylamine, to as high as at least 99.0% and 99.98%,respectively. The process also has the benefit of producing less thanabout 300 ppm of difficult to remove byproducts such as TMPDA and the 2°amine. Further improvements associated with the present inventioninclude lower operating costs, reduced waste generation, and reduceddisposal and treatment costs associated with such hydrogenationprocesses.

[0028] While the invention is directed to the process for the productionof 3-dimethylaminopropylamine, it is applicable to any amine includingaliphatic and aromatic amines and their derivatives, such ashexamethylene diamine, propyl amines, butyl amines, benzyl amines,tallow amines, ethyl amines, etc., produced from a nitrile includingaliphatic and aromatic nitrites and their derivatives such asproprionitrile, butyronitriles, tallow nitrites, acetonitriles, benzylnitrites, etc., in which finely divided catalyst is suspended in theliquid reaction medium.

[0029] Specifically, a process for production of3-dimethylaminopropylamine in high yield and selectivity may be carriedout at pressures of 45-500 psig, preferably 45-150 psig, and attemperatures of 70° to 100° C., by feeding hydrogen and nitrile into aliquid reaction medium containing, along with the amine produced, water,inorganic base and a finely divided nickel or cobalt catalyst dispersedin the liquid components of the reaction medium. The catalyst, whichpreferably is sponge (e.g. Raney®) nickel, with or without promotermetals such as chromium and/or iron, loses some of its activity duringhydrogenation.

[0030] To maintain a given level of catalytic activity within thecatalytic mass, it is necessary for the catalyst in the reaction mediumto be gradually regenerated as described by Cutchens, et al. in U.S.Pat. No. 4,429,159, which is incorporated herein by reference. Thisregeneration is effected by discharging a quantity of reaction mediumwhich contains catalyst into the regeneration vessel, allowing thecatalyst to settle, decanting the organic upper layer back to thereaction vessel, and washing the catalyst with water to removecontaminants from the catalyst before it is recycled to the reactor. Therecycled catalyst may consist of a mixture of fresh catalyst and ofrecycled catalyst if addition of a small amount of fresh catalyst isrequired to increase the catalyst activity in the reactor.

[0031] A key to the effectiveness of the low pressure diaminehydrogenation process of the present invention is the incorporation ofan effective amount of an inexpensive caustic hydroxide in the spongenickel catalyst to enhance the selectivity of the reaction. Thehydroxide is preferably a hydroxide of a Group IA (“alkali metal”)element of the periodic table, selected from the group consisting oflithium, sodium, potassium, rubidium, cesium, and mixtures thereof. Morepreferably, the caustic alkali metal hydroxide is sodium hydroxide,potassium hydroxide, cesium hydroxide, and mixtures thereof.

[0032] The catalyst suitable for use in the present invention is aRaney® type catalyst, also known as “skeletal” or “sponge-type” metalcatalysts. While both nickel and cobalt sponge catalysts are acceptablefor use, it is preferred to use a Raney® nickel catalyst with thepresent invention due to the higher cost associated with the use ofcobalt sponge catalysts.

[0033] The nickel catalyst used in the low-pressure hydrogenationprocess of the present invention is sponge nickel, or as it is oftenreferred to, Raney® nickel. The catalyst is commercially available froma number of sources (W.R. Grace and Co.; Degussa; Activated Metals), orit may be manufactured using any number of methods described in theliterature, for instance by Mozingo in Organic Syntheses CollectedVolume 3, p. 181; and Fieser and Fieser, Reagents for Organic Synthesis,Vol. 1, pp. 723-731 and references cited therein.

[0034] An alternative catalyst which may be used with the presentinvention is a cobalt catalyst. Such a cobalt catalyst used in thelow-pressure hydrogenation process of the present invention is spongecobalt, also known as Raney® cobalt. The catalyst is also availablecommercially from a number of sources, and may be obtained syntheticallyusing routes described in the literature.

[0035] Conventional promoters may be incorporated into or included withthe sponge catalyst in conventional amounts known to those of skill inthe art. Examples of such promoters suitable for incorporation into thecatalyst include Group VIa and Group VIII metals such as chromium, iron,molybdenum, and the like.

[0036] The N,N-dimethylaminopropionitrile (DMAPN) which is used as thestarting material (feedstock) in the present invention can be obtainedcommercially from a variety of sources (Acros; Aldrich Chemical Co.).Alternatively, DMAPN can be obtained synthetically by any of theprocesses known in the art, such as from the reaction of acrylonitrileand dimethylamine. A process of this type, namely the reaction ofdimethylamine with acrylonitrile in a blow column reactor, is describedin German Patent Specification No. 27 09 966. Preferably, for use in thepresent invention, the DMAPN is obtained from a commercial supplier andis significantly free of n-propylamine and diaminopropane.

[0037] The hydrogenation of DMAPN to DMAPA according to the presentinvention is conducted under conditions such that only a minimal amountof water is required for use within the reactor. The liquid portion ofthe reaction medium comprises two phases: an aqueous solution ofinorganic base, and an aqueous solution of the catalyst. The amount ofwater suitable for use with the reduction process is between about 0.1wt. % and about 10 wt. % of the weight of the reaction mixture,preferably about 2 wt. % of the reaction mixture. With respect to theratio of water to inorganic base, the preferred range ratio is 0.5 to 10moles of water to 1 mole of caustic alkali.

[0038] The reduction of the nitrile to the amine can be carried outunder hydrogen pressures from as low as about 45 psig to as high asabout 500 psig. However, the hydrogenation of DMAPN to DMAPA ispreferably carried out under a hydrogen pressure of from 45 to 300 psig,more preferably at a pressure from 45 to 150 psig or at a pressure from45 to 110 psig. The reduction of the nitrile to the amine is preferablycarried out at temperatures of between about 70° C. to about 100° C.,more preferably at temperatures between about 80° C. to about 100° C.,and still more preferably at temperatures between 85° C. and 95° C. Mostpreferably, the reduction of DMAPN to DMAPA is carried out at about 100psig and about 90° C.

[0039] As described herein, the pressure is measured in psig (pounds persquare inch, gauge), wherein 1 psig=0.068 atm (or 0.069 bar).Consequently, the reduction of the nitrile to the amine according to thepresent invention is preferably carried out under a hydrogen pressure offrom about 3.0 atm to about 10.2 atm.

[0040] The process described herein for the hydrogenation ofN,N-dimethylaminopropionitrile to N,N-dimethylaminopropylamine has theability to effect the conversion of the nitrile group to the primaryamine in surprisingly high selectivity and yield while minimizing oravoiding secondary amine byproduct formation over the course of thereaction. Consequently, the product amine, DMAPA, is produced with aselectivity of greater than 99.90%, and is produced in a yield of atleast 99% (based on starting DMAPN). As described herein, selectivityrefers to the amount of DMAPA formed from DMAPN, including the formationof byproducts that can be generated during the course of the reaction.Specifically, the process of the present invention preferably exhibits aselectivity of at least 99.60% of DMAPN to DMAPA, more preferablyexhibits a selectivity of at least 99.70% of DMAPN to DMAPA, and stillmore preferably exhibits a selectivity of at least 99.90% of DMAPN toDMAPA. The yield of DMAPA produced according to the present invention ispreferably at least 99% based on starting DMAPN, and can be about 99.1%,about 99.2%, about 99.3%, about 99.4%, about 99.5%, about 99.6%, about99.7%, about 99.8%, and about 99.9% based on the starting nitrile. Mostpreferably, the process of the present invention exhibits a selectivityof at least 99.98% and in a yield of at least 99% fromN,N-dimethylaminopropionitrile.

[0041] The hydrogenation can be conducted in any conventionalhydrogenation equipment suitable to effect the conversion. For example,suitable equipment includes, but is not limited to, a stirred tank orloop reactor, a continuous stirred tank reactor, a continuous gas liftreactor, a fixed-bed reactor, a trickle-bed reactor, a bubble-columnreactor, or a sieve-tray reactor. Preferred methods of operation includethose described in U.S. Pat. No. 6,281,388, which is incorporated hereinin its entirety.

[0042] The present invention is also envisioned to be applicable toother hydrogenation processes which typically use high pressures andtemperatures and sponge, or Raney®-type catalysts. Specific examples ofsuch processes which are envisioned to be applicable are those processeswhich utilize a mixture containing Raney® nickel catalyst and a strongcaustic base. Such processes would be expected to yield improvementssimilar to those described herein for the low-pressure hydrogenation ofDMAPN to DMAPA. For example, the low-pressure hydrogenation ofadiponitrile to hexamethylenediamine would be expected to yieldsimilarly improved results.

[0043] The following examples are included to demonstrate preferredembodiments of the invention. It should be appreciated by those of skillin the art that the techniques disclosed in the examples which followrepresent techniques discovered by the inventors to function well in thepractice of the invention, and thus can be considered to constitutepreferred modes for its practice. However, those of skill in the artshould, in light of the present disclosure, appreciate that many changescan be made in the specific embodiments which are disclosed and stillobtain a like or similar result without departing from the spirit andscope of the invention.

EXAMPLES Example 1 Preparation of Caustic

[0044] Caustic preparation begins with obtaining distilled water thathas been boiled to remove dissolved carbon dioxide. Caustic solutionsare prepared in about 25 wt. % in 100 gram batches by weight. Thecaustic (KOH, NaOH, etc.) is added to the degassed water (˜60 mL) withstirring. After complete dissolution of the caustic, additional water isadded to bring the weight of the solution to a total weight of 100grams. The solution is filtered, and stored in a closed container untiluse in order to minimize adsorption of CO₂ from the air.

Example 2 Hydrogenation Procedure

[0045] A one-liter autoclave reactor equipped with double turbineblades, dispersimax-type agitator, a coil extending to the bottom tocirculate the transfer fluid from a temperature controlled bath fortemperature control, and a fritted, stainless steel metal sample portbelow the liquid level is used to react hydrogen with3-(dimethylamino)propionitrile. Hydrogen is fed from a cylinder equippedwith a pressure gauge and a regulator to add hydrogen to the reactorwhen the pressure drops below the set pressure. The hydrogen flowsthough a mass flow meter. The 3-(dimethylamino)propionitrile (Acros) ispumped to the autoclave with an Isco Model 500D syringe pump. To theautoclave is charged 37.5 grams of sponge nickel catalyst (DegussaMC502) with iron and chromium added to promote the hydrogenationreaction (the catalyst contains about 85% nickel, 10% aluminum, 2%chromium, and 2% iron). The catalyst is washed 3 times with water and 3times with 3-dimethylaminopropylamine (Acros; contaminated with 72 ppmTMPDA by GC analysis), each wash consisting of mixed catalyst andmaterial in a 100 L graduated cylinder, settling the catalyst, anddecanting the top 50 mL of clear liquid. The catalyst, water, and3-dimethylaminopropylamine slurry amounting to 50 mL are then charged tothe autoclave. Additionally, 265 mL of 100% 3-dimethylaminopropylamineand 6 mL of 25% (wt.) caustic solution in water is charged. The causticsolution is a blend containing 50 wt. % sodium hydroxide and 50 wt. %potassium hydroxide. The agitator is turned on, and the autoclave heatedto 60° C. The autoclave is then purged three times with nitrogen, andthen three times with hydrogen, before being pressurized to 7.805 atmwith hydrogen. The autoclave is then heated to 90° C., and the pressuredchecked and maintained for 5 minutes.

[0046] The feed of 3-(dimethylamino)propionitrile containing 0.04 wt. %water is then started to the autoclave at a rate of 5 mL/minute usingthe syringe pump. Pressure and temperature are maintained at 7.805 atmand 90° C., respectively, during the entirety of the run. After 27minutes, the feed is stopped, and a 150 g sample is withdrawn from theautoclave for analysis. The feed is then resumed under the sameconditions as before. This procedure is then repeated for a total of 7cycles.

[0047] The reaction mixture was sampled after each cycle and analyzedfor purity, reaction progress, and the presence and amount ofby-products (if any) formed. Analysis was by gas chromatography (HP 5890Series II; Phenomenex Zebron ZB-1 capillary column Phenomenex Cat. No.7HK-G001-36) with flame ionization detection in order to quantify theby-product impurities. Analysis of the cycles and the product are givenin Table 1 TABLE 1 Product analysis, per cycle. Amounts of ByproductsUsing External Standard Calibration, ppm dmapn tmpda 2° amine Cycle n-pappm dap ppm ppm ppm ppm water ppm 1 89 0 0 43 200 7.26 2 123 0 0 29 2674.72 3 143 0 0 17 284 3.47 4 174 0 0 14 308 2.65 5 190 0 0 7 265 2.11 6209 0 0 5 236 1.71 7 223 0 0 0 214 1.37

[0048] Table 1 shows that the amount of secondary amine remainsgenerally at or below 300 ppm over the course of the entire reactionwhen DMAPN was hydrogenated utilizing a sponge nickel catalyst and aGroup IA alkali metal hydroxide according to the of the presentinvention. The amount of TMPDA formed, stemming from es found in thefeed DMAPA used to prepare the catalyst slurry, decreased over thecourse of the reaction, resulting in the final product being free ofthis common and difficult to remove by-product.

[0049] As is evident from the data shown in Table 1, the product3-(dimethylamino)propylamine results in a molar yield of 99.98% with apurity of >99% and no TMPDA or other secondary amine impurity and lessthan 300 ppm of the secondary amine present in the final product.

Example 3 Hydrogenation of DMAPN Over Sponge Nickel with DifferentAlkali Metal Hydroxides Added

[0050] A series of runs was carried out to determine the effect ofvarious alkali metal hydroxide additions to a sponge nickel catalyst forthe hydrogenation using the same procedures detailed in examples 1 and2. The 50 wt. % sodium hydroxide and 50 wt. % potassium hydroxidecaustic solution specified in example 2 was substituted with an aqueoussolution of the alkali metal hydroxide at the level indicated in Table2. After the reaction number of cycles indicated in Table 2, a samplewas removed for gc analysis. The amount of DMAPN remaining and theamount of various secondary amine side products generated was recorded.The conditions and results are clearly shown in Table 2. TABLE 2 Effectof Alkali Metal Hydroxide n Activity and Selectivity Metal Number DMAPN2° Amt. Alkali Metal Hydroxide Temp./Press. of Remaining amine RunCatalyst Catalyst Hydroxide Amount ° C./psig Cycles (ppm) (ppm) 1Ni-MC502 37.5 g NaOH  8 mL of 25% 90/110 6 163 1440 (wt) aqueous NaOH 2Ni-MC502 37.5 g KOH  6 mL of 25% 90/100 6 0 9 (wt) aqueous KOH 3Ni-MC502 37.5 g RbOH  7 mL of 25% 90/100 6 0 1463 (wt) aqueous RbOH 4Ni-MC502 37.5 g CsOH  8 mL of 25% 90/500 6 0 15 (wt) aqueous CsOH 5Ni-MC502 37.5 g LiOH 80 mL of 10% 90/500 6 0 2567 (wt) aqueous LiOH 6Ni-MC502 37.5 g KOH/NaOH  6 mL of 25% 90/100 6 0 9 (wt) aqueous 50/50NaOH/KOH

[0051] Tables 1 and 2 clearly show that the use of such alkali metalhydroxides as KOH, CsOH, and mixtures of KOH/NaOH allowed the reactionto proceed to a high DMAPN conversion, e.g., a low DMAPN concentrationremained in the product DMAPA within a reasonable time and alsomaintaining a high selectivity for the primary amine. The use of LiOH(run 5) showed a poor improvement in the amount of side-productformation using the same catalyst as in the other tests. From theseresults, to maintain a high rate of selectivity in the hydrogenation ofdimethylaminopropionitrile to dimethylaminopropylamine, KOH, CsOH, andmixtures of KOH/NaOH are most effective as alkali metal hydroxides.

[0052] All of the methods and processes disclosed and claimed herein canbe made and executed without undue experimentation in light of thepresent disclosure. While the methods of this invention have beendescribed in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to the methodsand/or processes and in the steps or in the sequence of steps of themethods described herein without departing from the concept, spirit andscope of the invention. More specifically, it will be apparent thatcertain agents which are chemically related may be substituted for theagents described herein while the same or similar results would beachieved. All such similar substitutes and modifications apparent tothose skilled in the art are deemed to be within the spirit, scope andconcept of the invention.

What is claimed is:
 1. A process for the production ofN,N-dimethylaminopropylamine from N,N-dimethylaminopropionitrile by lowpressure hydrogenation comprising: feeding hydrogen andN,N-dimethylaminopropionitrile into a low-pressure reactor containing asponge nickel catalyst, at least one Group IA alkali metal hydroxide,and water to form a reaction medium; heating the reaction medium to atemperature of about 70° C. to about 100° C.; pressurizing the reactorto a pressure of about 45 psig to about 500 psig; and hydrogenating thenitrile to form N,N-dimethylaminopropylamine,
 2. The process of claim 1,wherein the selectivity of N,N-dimethylaminopropionitrile toN,N-dimethylaminopropylamine is greater than about 99.60%.
 3. Theprocess of claim 1, wherein the selectivity ofN,N-dimethylaminopropionitrile to N,N-dimethylaminopropylamine isgreater than about 99.90%.
 4. The process of claim 1, wherein the GroupIA alkali metal hydroxide is selected from the group consisting ofsodium hydroxide, potassium hydroxide, rubidium hydroxide, cesiumhydroxide and mixtures thereof.
 5. The process of claim 1 wherein theGroup IA alkali metal hydroxide is potassium hydroxide.
 6. The processof claim 1 wherein the Group IA alkali metal hydroxide is sodiumhydroxide.
 7. The process of claim 1 wherein the Group IA alkali metalhydroxide is a mixture of sodium hydroxide and potassium hydroxide. 8.The process according to claim 1 wherein the temperature is between 85°C. and 95° C.
 9. The process of claim 1 wherein the pressure is between45 psig and 300 psig
 10. The process of claim 1 wherein the pressure isbetween 45 psig and 150 psig.
 11. The process of claim 1 wherein thepressure is between 45 psig and 110 psig.
 12. The process of claim 1wherein the amount of water is about 0.1 wt. % to about 10 wt. % of thereaction medium.
 13. A process for the production ofN,N-dimethylaminopropylamine from N,N-dimethylaminopropionitrile by lowpressure hydrogenation comprising: feeding hydrogen andN,N-dimethylaminopropionitrile into a low-pressure reactor containing acatalyst, at least one Group IA alkali metal hydroxide, and water toform a reaction medium; heating the reaction medium to a temperature ofabout 70° C. to about 100° C.; pressurizing the reactor to a pressure ofabout 45 psig to about 150 psig; and hydrogenating the nitrile to formN,N-dimethylaminopropylamine.
 14. The process of claim 13, wherein thecatalyst is a sponge nickel catalyst.
 15. The process of claim 13,wherein the catalyst is a cobalt catalyst.